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4.67

Date Code 20100129

Instruction Manual

SEL-751A Relay

Protection and Logic Functions

Reclose Logic

for the case of an instantaneous trip, but the circuit breaker status
indication is slow—the instantaneous trip (reclose initiation) occurs
before the SEL-751A sees the circuit breaker close.

If a flashover occurs in a circuit breaker tank during an open interval
(circuit breaker open and the SEL-751A calls for a trip), the SEL-751A
goes immediately to lockout.

EXAMPLE 4.8

Additional Settings Example

The preceding settings example initiates open interval timing on
rising edge of the TRIP Relay Word bit. The following is an example of
reclose initiation on the opening of the circuit breaker.

Presume input

IN101

is connected to a 52a circuit breaker auxiliary

contact (52A := IN101).

With setting:
79RI :=

NOT 52A

the transition of the 52A Relay Word bit from logical 1 to logical 0
(breaker opening) initiates open interval timing. Setting 79RI looks
for a logical 0 to logical 1 transition, thus Relay Word bit 52A is
inverted in the 79RI setting.

The reclose initiate supervision setting 79RIS supervises setting 79RI.
With settings:
79RI :=

NOT 52A

79RIS :=

TRIP

the transition of the 52A Relay Word bit from logical 1 to logical 0
initiates open interval timing only if the TRIP Relay Word bit is at
logical 1 (TRIP = logical 1). Thus, the TRIP Relay Word bit has to be
asserted when the circuit breaker opens in order to initiate open
interval timing. With a long enough setting of the Minimum Trip
Duration Timer (TDURD), the TRIP Relay Word bit will still be asserted
to logical 1 when the circuit breaker opens (see

Figure 4.29

If the TRIP Relay Word bit is at logical 0 (TRIP = logical 0) when the
circuit breaker opens (logical 1 to logical 0 transition), the relay goes
to the Lockout State. This helps prevent reclose initiation for circuit
breaker openings caused by trips external to the relay.

If circuit breaker status indication (52A) is slow, additional setting
change ULCL := 0 (unlatch close; refer to

Figure 4.30

and

accompanying explanation) may need to be made when 79RI := NOT
52A. ULCL := 0 avoids going to lockout prematurely for an
instantaneous trip after an auto-reclose by not turning CLOSE off
until the circuit breaker status indication tells the relay that the
breaker is closed. The circuit breaker anti-pump circuitry should take
care of the TRIP and CLOSE being on together for a short period of
time.

Other Settings Considerations

Example 4.8

the preceding additional setting example, the reclose initiate

setting (79RI) includes input

IN101

, that is connected to a 52a breaker auxiliary

contact (52A := IN101).

79RI :=

NOT 52A

If a 52b breaker auxiliary contact is connected to input

IN101

(52A := NOT

IN101), the reclose initiate setting (79RI) remains the same.

If no reclose initiate supervision is desired, make the following setting:

79RIS :=

(numeral 1)

Setting 79RIS := logical 1 at all times. Any time a logical 0 to logical 1
transition is detected by setting 79RI, open interval timing will be initiated
(unless prevented by other means).

Sel 751A, Instruction Manual

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